Beam focusing lenses for focusing light from a semiconductor laser are known. For example, Japanese Laid-Open Patent Applications S57-176014 and 2001-188151 disclose beam focusing lenses that include two cylindrical lenses with orthogonal axes of symmetry that collect and focus light beams that have different angles of divergence in directions orthogonal to their optical axes from a semiconductor laser. The beam focusing lenses provide circular or nearly circular output beams.
However, in practice, the two cylindrical lenses with the axes of symmetry orthogonal to one another do not always efficiently collect the diverging light from the light source. FIG. 12 is a light spot diagram of light collected by such a prior art beam focusing lens. The two cylindrical lenses collect light diverging in cross-sections in which the cylindrical surfaces have refractive powers. However, light diverging in other directions is not adequately collected. As shown in FIG. 12, light collection is insufficient at the angles of 45 degrees in relation to the horizontal and vertical directions of FIG. 12 that correspond to the directions of the axes of symmetry and of maximum refractive power of the cylindrical lenses, especially at distances farther from the center of light collection.
Using more cylindrical lenses to efficiently collect light in the directions in which light collection is insufficient as described above is impractical because of the complexity of designing and adjusting optical systems with more cylindrical lenses.